This invention relates to a composite, break-resistant sewing thread and a method of manufacturing the sewing thread. The product and method departs from prior art yarns and methods in that the product is intended to produce a relatively hard, high-twist yarn rather than a soft, low-twist yarn. Prior art core-spun yarns are produced with staple fibers on the surface of the composite yarn in order to soften the feel of the yarn and provide a yarn which resembles ring-spun, 100% staple-fiber yarns. Thus, feel and appearance are the principal factors determining the design and production of the yarn. Such yarns generally have a relatively high degree of elongation.
In contrast, sewing thread must be strong and relatively inelastic. This has been accomplished in the prior art by ring-spinning sewing thread with 100% cotton, blends of cotton and staple synthetic fibers such as polyester, or 100% staple synthetic fibers, with the insertion of high twist. This imparts to the sewing thread a hard finish and reduces elongation, making the yarn susceptible to breakage. Achieving a proper balance between the twist necessary to impart additional strength and too much twist which can increase breakage under certain processing conditions has been a continuing problem in the manufacture of conventional sewing thread.
One solution to this problem has been to utilize high tenacity filament sewing thread thereby avoiding the use of staple fibers altogether. While such filament sewing threads can be made very break-resistant, they also have disadvantages, including a slick, cheap appearance, short, stiff cut ends which can irritate the skin of the wearer of garments made with the thread, and sensitivity to heat, friction and abrasion which can soften and elongate the yarn, and, in extreme cases, cause the yarn to separate.
Manufacturers who purchase and use sewing thread monitor thread break frequency and return thread or demand refund or credit for yarn which exceeds maximum thread break standards. This, of course, raises the cost to the thread manufacturer of producing the thread and can result in loss of business or good will. The present invention provides a sewing thread which can be efficiently manufactured with consistent quality and which provides superior performance.
Therefore, it is an object of the invention to provide a composite, break-resistant sewing thread which has enhanced resistance to breakage.
It is another object of the invention to provide a composite, break-resistant sewing thread which has a high-strength core yarn.
It is another object of the invention to provide a composite, break-resistant sewing thread which has a high-strength core yarn and a staple fiber cover yarn which protects the core yarn from heat and friction.
It is another object of the invention to provide a composite, break-resistant sewing thread which can be made in a continuous process on an air-jet spinning machine.
It is another object of the invention to provide a method for manufacturing a composite yarn, including a sewing thread, which has improved processing and use characteristics.
These and other objects of the present invention are achieved in the preferred embodiments disclosed below by providing a composite, break-resistant sewing thread, comprising a core comprising a continuous filament, non-stretch high-tenacity synthetic yarn and a cover comprising drafted staple fibers air-jet twisted around and covering the core for protecting the core from heat and friction during a sewing operation.
According to one preferred embodiment of the invention, the core comprises at least 55 percent of the total weight of the composite thread.
According to another preferred embodiment of the invention, the core is a fully-oriented polyester yarn.
According to yet another preferred embodiment of the invention, the yarn includes a second core yam plied with the core yarn.
According to yet another preferred embodiment of the invention, the core is a fully-oriented polyester yarn having a denier between 60 and 250.
According to yet another preferred embodiment of the invention, the cover is polyester.
According to yet another preferred embodiment of the invention, the cover is cotton.
According to yet another preferred embodiment of the invention, the core comprises at least 60 percent of the total weight of the composite thread.
According to yet another preferred embodiment of the invention, the core comprises at least 76 percent of the total weight of the composite thread.
An embodiment of the method of producing a composite, break-resistant non-stretch sewing thread according to the invention comprises the steps of feeding a sliver of staple fibers through a plurality of successive drafting zones, introducing a continuous filament, high-tenacity synthetic yarn into the sliver downstream of the drafting zones and upstream of an air-jet spinning zone, air-jet spinning the sliver in the air-jet spinning zone around the continuous filament yarn to form a core comprising the continuous filament yarn covered with staple fibers comprising a cover for protecting the core from heat and friction during a sewing operation.
According to one preferred embodiment of the invention, the method includes the steps of doubling two yarns produced according to the method and twisting the doubled yarn to form a two-ply twisted yarn.